1. Field of the Invention
The present invention relates to the field of medical diagnostic systems, particularly to a system for determining and predicting individual skin-damaging levels of ultraviolet (UV) radiation.
2. Description of Prior Art
Solar radiation reaching the earth consists of electromagnetic energy ranging from ultraviolet (UV) radiation to infrared (IR) radiation. UV radiation is further subdivided into three types: UV-A, UV-B, and UV-C. UV-C radiation are those wavelengths in the range of 200 to 285 nanometers (nm); it is totally absorbed by the earth's atmosphere. UV-B, from about 285 to 318 nm, is known to cause skin cancer in humans. UV-A, from about 315 to 400 nm, is mostly responsible for tanning. However, UV-A has also been found to play a role in skin cancer and is the cause of eye cataracts, solar retinitis, and corneal dystrophies.
In view of the latest problems associated with global warming and development of holes in the ozone layer of the earth atmosphere, the risk of development of skin cancer and other diseases caused by intensified exposure to solar radiation is greatly increasing.
Based on general principles and techniques for radiometry and photometry, several UV radiation-measuring and warning instruments have been developed and made commercially available.
A personal UV radiometer, described in U.S. Pat. No. 5,008,548 to Nahum Gat, 1991, includes an LCD display, a photocell, and an integrated circuit for processing user inputs and UV radiation data.
However, this device of U.S. Pat. No. 5,008,548 does not take into account the changes in skin pigmentation which occur while a person is being exposed to solar radiation. Furthermore, this device is not convenient, since it is intended for attachment to an article of clothing and may restrict movement of a subject during rigorous physical activity, for instance, a volleyball game.
An apparatus, disclosed in U.S. Pat. No. 4,985,632 to Frank Bianco et al., 1991, comprises an electronic wristwatch having a digital readout for displaying the time, the day, and the month. It also incorporates a photodiode for detecting skin-damaging UV radiation, a microcomputer, and four function buttons.
This device, however, is not user-friendly due to its large number of functions, many of which are superfluous. Moreover, like the radiometer, the wristwatch does not take into account skin pigmentation changes which occur during exposure to UV radiation. Furthermore, it cannot monitor UV radiation when placed in the shade.
Furthermore, all of the above prior-art devices are based on the assumption that the amount of UV radiation that may be safely tolerated by human skin is independent of the rate at which such incident radiation is accumulated. These prior art devices measure only the cumulative magnitude of incident UV radiation, and do not factor any rate measurements into the determination of a safe UV-radiation threshold.
In other words, if one of two identical cumulative UV-radiation doses is an intense dose received relatively quickly and the other a longer-duration exposure of lesser intensity, none of the prior-art devices are able to distinguish between these two doses with respect to relative differences in potential harmful effect on the skin. The prior-art devices cannot monitor differences in UV-radiation exposure rates.
The concept of total accumulated UV radiation as the single measure of the effect on human skin of exposure to UV radiation is flawed in principle for two major reasons. Firstly, as embodied in the prior-art devices, the cumulative dose that is monitored does not differentiate between the two most important constituent spectral ranges within the overall UV-radiation spectrum: UV-A and UV-B. These constituent UV-radiation spectra each have specific and differing effects on human tissue ranging from the propagation of skin cancer to cataract formation. Therefore, each of these spectral ranges deserves separate monitoring, data collection and analysis.
Secondly, as discussed above, data on cumulative dosage only without consideration of UV-exposure rates, i.e., the intensity of incident UV-radiation reaching the detector per unit time, cannot properly distinguish between harmful and unharmful UV exposures. The practice of measuring only accumulated UV radiation stems from the use of the Geiger counter for measuring radioactive dosage. The measurement of cumulative radioactivity received by a human body is a proper measurement because the harmful effect of radioactivity on human tissue is, in fact, a cumulative one: no matter what the rate of exposure, once the maximum cumulative threshold of exposure is reached, the damage is irreversibly done.
However, such is not the case with accumulated solar radiation. Solar radiation can be accumulated in large doses without harm if the dose is accumulated over a sufficiently long period of time. Equivalent cumulative dosages might be received in one day or one month. In the first case, the dose could be dangerous, whereas in the second case it might be completely benign. Therefore, data collected only for cumulative radiation exposure is neither indicative of actual skin damage done, nor predictive with respect to future harmful effects on the tissue.
To initiate a solution to these problems of effective UV radiation monitoring and analysis, the inventors submitting the present application developed a special noseshade for monitoring both cumulative UV-A and UV-B radiation exposure. This noseshade is fully described in U.S. patent application Ser. No. 867,433 filed Apr. 13, 1992, now U.S. Pat. No. 5,151,600. However, the noseshade is not intended for the analysis of recorded data, not does it interface to a radiation exposure analyzer.